feat(miniflare): add getWorkerdFeatureFlags() for compatibility flag resolution

Add a TypeScript implementation that replicates workerd's C++ compileCompatibilityFlags()
function. This computes which compatibility flags are enabled based on:
- Compatibility date (flags enabled after their compatEnableDate)
- Explicit compatibility flags (enable/disable overrides)
- Implied flags (cascading dependencies between flags)

Files added:
- scripts/build-capnp-compat.mjs: Build script that downloads compatibility-date.capnp
  from workerd, compiles it with capnp-es, and extracts annotation metadata
- src/shared/compatibility-date.ts: Cap'n Proto types generated by capnp-es
- src/shared/compatibility-flags-metadata.ts: Extracted annotation metadata
- src/shared/compatibility-flags.ts: Main implementation with getWorkerdFeatureFlags()
- test/shared/compatibility-flags.spec.ts: Test suite

Also updates:
- package.json: Added capnp:compat script
- tsconfig.json: Include the build script for type checking
- GitHub workflow: Auto-regenerate compatibility flags on workerd dependency updates

Author: petebacondarwin

.github/workflows/miniflare-dependabot-versioning-prs.yml

@@ -12,7 +12,7 @@ permissions:
 
 jobs:
   generate-changeset:
-    runs-on: ubuntu-slim
+    runs-on: ubuntu-latest
     if: |
       github.event.pull_request.user.login == 'dependabot[bot]'
     steps:
@@ -26,11 +26,29 @@ jobs:
       - name: Install Dependencies
         uses: ./.github/actions/install-dependencies
 
+      - name: Install Cap'n Proto compiler
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y capnproto
+
       - name: Configure Git
         run: |
           git config --global user.email wrangler@cloudflare.com
           git config --global user.name 'Wrangler automated PR updater'
 
+      - name: Regenerate compatibility flags
+        run: |
+          pnpm --filter miniflare run capnp:compat
+
+          # Commit the regenerated files if there are changes
+          git add packages/miniflare/src/shared/compatibility-date.ts packages/miniflare/src/shared/compatibility-flags-metadata.ts
+          if git diff --cached --quiet; then
+            echo "No changes to compatibility flags files"
+          else
+            git commit -m "chore(miniflare): regenerate compatibility flags for workerd update"
+            git push
+          fi
+
       - name: Generate Miniflare changesets
         # The paremeters to the script are:
         # - PR: The number of the current Dependabot PR

packages/miniflare/package.json

@@ -31,6 +31,7 @@
 	],
 	"scripts": {
 		"build": "node scripts/build.mjs && pnpm run types:build",
+		"capnp:compat": "node scripts/build-capnp-compat.mjs",
 		"capnp:workerd": "node scripts/build-capnp.mjs",
 		"check:lint": "eslint --max-warnings=0 \"{src,test}/**/*.ts\" \"types/**/*.ts\"",
 		"check:type": "tsc",